The Stirling engine was originally conceived as long ago as 1816 by Rev. Stirling. During the middle of the 19th. Century, commercial applications of this hot gas engine were devised to provide rotary power to mills; these were fixed power plants. The Stirling engine was ignored thereafter until the middle of the 20th. Century because of the usefulness and popularity of the internal combustion engine. Not until very recently has the Stirling engine been visualized as a power plant to motorize moving vehicles. Converting a Stirling engine to automotive use presents many formidable problems due to reduced weight, size, energy conservation, cost and reliability limitations that are placed upon it.
One of these problems, energy conservation (engine efficiency), has stimulated the introduction of several modifications to make the Stirling engine suitable for automotive use. The Stirling engine employs a continuously operating external heating circuit which tends to waste considerable energy via exhaust gases released to atmosphere. For fixed power plants of the Stirling type, heavy steel heat exchangers were previously devised to return a proportion of the exhaust heat energy to the inducted air to facilitate combustion. Upon conversion to automotive use, the heavy steel heat exchangers were replaced by rotary ceramic preheaters which earlier had found utility in gas turbine engine applications. The rotary preheater functioned to expose hot gases through a crescent shaped opening (a one-half circle) to a rotating ceramic wheel, and separately exposed inducted air to the heated wheel at an independent crescent shaped opening.
Although the new art of making uni-directional ceramic heat exchanger cores was most welcome, certain attendant problems were not welcome, such as cost of the crescent shaped seals, the energy loss and noise from the motor drive, the decrease of reliability due to mechanical stress placed upon the fragile ceramic core by dynamic rubbing seal contact, and the lack of a uniform heat flux into the heater tube array due to the non-uniform air flow entering the combustor from the preheater.